{"id":2610,"date":"2025-03-11T23:28:24","date_gmt":"2025-03-11T15:28:24","guid":{"rendered":"https:\/\/www.laixuexila.com\/?p=2610"},"modified":"2025-03-11T23:28:24","modified_gmt":"2025-03-11T15:28:24","slug":"postgresql-select-%e8%af%ad%e5%8f%a5%e8%af%a6%e8%a7%a3","status":"publish","type":"post","link":"https:\/\/www.laixuexila.com\/index.php\/2025\/03\/11\/postgresql-select-%e8%af%ad%e5%8f%a5%e8%af%a6%e8%a7%a3\/","title":{"rendered":"PostgreSQL SELECT \u8bed\u53e5\u8be6\u89e3"},"content":{"rendered":"\n

SELECT<\/code> \u8bed\u53e5\u7528\u4e8e\u4ece PostgreSQL \u6570\u636e\u5e93\u4e2d\u67e5\u8be2\u6570\u636e\uff0c\u662f SQL \u4e2d\u6700\u5e38\u7528\u7684\u67e5\u8be2\u8bed\u53e5\u3002PostgreSQL \u63d0\u4f9b\u4e86\u5f3a\u5927\u7684 SELECT<\/code> \u529f\u80fd\uff0c\u5305\u62ec\u57fa\u7840\u67e5\u8be2\u3001\u6761\u4ef6\u8fc7\u6ee4\u3001\u6392\u5e8f\u3001\u5206\u7ec4\u3001\u8fde\u63a5\u3001\u591a\u8868\u67e5\u8be2\u3001\u5b50\u67e5\u8be2\u7b49\u3002<\/p>\n\n\n\n

\n\n\n\n

1. SELECT<\/code> \u8bed\u6cd5<\/strong><\/h2>\n\n\n\n

1.1 \u57fa\u672c\u8bed\u6cd5<\/strong><\/h3>\n\n\n\n
SELECT column1, column2, ... \nFROM table_name;<\/code><\/pre>\n\n\n\n
    \n
  • column1, column2, ...<\/code>\uff1a\u8981\u67e5\u8be2\u7684\u5217\u3002<\/li>\n\n\n\n
  • table_name<\/code>\uff1a\u67e5\u8be2\u7684\u6570\u636e\u8868\u3002<\/li>\n<\/ul>\n\n\n\n
    \u5982\u679c\u8981\u67e5\u8be2\u8868\u4e2d\u7684\u6240\u6709\u5217\uff0c\u53ef\u4ee5\u4f7f\u7528 *<\/code>\uff1a<\/p>\n\n\n\n
    SELECT * FROM table_name;<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    2. \u57fa\u7840\u67e5\u8be2\u793a\u4f8b<\/strong><\/h2>\n\n\n\n
    \u5047\u8bbe\u6709\u4e00\u4e2a employees<\/code> \u8868\uff1a<\/p>\n\n\n\n
    CREATE TABLE employees (\n    id SERIAL PRIMARY KEY,\n    name VARCHAR(100),\n    age INT,\n    department VARCHAR(50),\n    salary DECIMAL(10,2)\n);<\/code><\/pre>\n\n\n\n
    \u63d2\u5165\u793a\u4f8b\u6570\u636e\uff1a<\/p>\n\n\n\n
    INSERT INTO employees (name, age, department, salary) VALUES\n('Alice', 30, 'HR', 5000.00),\n('Bob', 25, 'IT', 6000.00),\n('Charlie', 35, 'Finance', 7000.00);<\/code><\/pre>\n\n\n\n
    \u6267\u884c\u67e5\u8be2\uff1a<\/p>\n\n\n\n
    SELECT * FROM employees;<\/code><\/pre>\n\n\n\n
    \u7ed3\u679c\uff1a<\/p>\n\n\n\n
     id |  name   | age | department | salary\n----+---------+-----+------------+--------\n  1 | Alice   |  30 | HR         | 5000.00\n  2 | Bob     |  25 | IT         | 6000.00\n  3 | Charlie |  35 | Finance    | 7000.00<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    3. \u6761\u4ef6\u67e5\u8be2 (WHERE<\/code> \u5b50\u53e5)<\/strong><\/h2>\n\n\n\n
    WHERE<\/code> \u8bed\u53e5\u7528\u4e8e\u8fc7\u6ee4\u6570\u636e\uff1a<\/p>\n\n\n\n
    SELECT * FROM employees WHERE age > 30;<\/code><\/pre>\n\n\n\n
    \u67e5\u8be2 age > 30<\/code> \u7684\u5458\u5de5\uff1a<\/p>\n\n\n\n
     id |  name   | age | department | salary\n----+---------+-----+------------+--------\n  3 | Charlie |  35 | Finance    | 7000.00<\/code><\/pre>\n\n\n\n
    3.1 \u7ed3\u5408 AND<\/code> \u548c OR<\/code><\/strong><\/h3>\n\n\n\n
    SELECT * FROM employees WHERE age > 25 AND department = 'IT';<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    4. \u6392\u5e8f\u67e5\u8be2 (ORDER BY<\/code>)<\/strong><\/h2>\n\n\n\n
    ORDER BY<\/code> \u7528\u4e8e\u5bf9\u7ed3\u679c\u8fdb\u884c\u6392\u5e8f\uff1a<\/p>\n\n\n\n
    SELECT * FROM employees ORDER BY salary DESC;<\/code><\/pre>\n\n\n\n
    \u6309 salary<\/code> \u964d\u5e8f\u6392\u5e8f\uff1a<\/p>\n\n\n\n
     id |  name   | age | department | salary\n----+---------+-----+------------+--------\n  3 | Charlie |  35 | Finance    | 7000.00\n  2 | Bob     |  25 | IT         | 6000.00\n  1 | Alice   |  30 | HR         | 5000.00<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    5. \u9650\u5236\u67e5\u8be2\u7ed3\u679c (LIMIT<\/code> \u548c OFFSET<\/code>)<\/strong><\/h2>\n\n\n\n
    5.1 \u9650\u5236\u8fd4\u56de\u7684\u884c\u6570<\/strong><\/h3>\n\n\n\n
    SELECT * FROM employees LIMIT 2;<\/code><\/pre>\n\n\n\n
    \u8fd4\u56de\u524d 2 \u884c\u6570\u636e\u3002<\/p>\n\n\n\n
    5.2 \u8df3\u8fc7\u524d\u51e0\u884c<\/strong><\/h3>\n\n\n\n
    SELECT * FROM employees ORDER BY salary DESC LIMIT 2 OFFSET 1;<\/code><\/pre>\n\n\n\n
    \u8df3\u8fc7 1 \u884c\uff0c\u8fd4\u56de 2 \u884c\u6570\u636e\u3002<\/p>\n\n\n\n
    \n\n\n\n
    6. \u8ba1\u7b97\u603b\u6570 (COUNT<\/code>)<\/strong><\/h2>\n\n\n\n
    \u67e5\u8be2\u5458\u5de5\u603b\u6570\uff1a<\/p>\n\n\n\n
    SELECT COUNT(*) FROM employees;<\/code><\/pre>\n\n\n\n
     count\n-------\n     3<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    7. \u5206\u7ec4\u67e5\u8be2 (GROUP BY<\/code> \u548c HAVING<\/code>)<\/strong><\/h2>\n\n\n\n
    GROUP BY<\/code> \u7528\u4e8e\u6309\u67d0\u5217\u5206\u7ec4\uff0cHAVING<\/code> \u8fc7\u6ee4\u5206\u7ec4\u540e\u7684\u7ed3\u679c\u3002<\/p>\n\n\n\n
    \u7edf\u8ba1\u6bcf\u4e2a\u90e8\u95e8\u7684\u5e73\u5747\u5de5\u8d44\uff1a<\/p>\n\n\n\n
    SELECT department, AVG(salary) FROM employees GROUP BY department;<\/code><\/pre>\n\n\n\n
     department |  avg  \n------------+-------\n HR         | 5000.00\n IT         | 6000.00\n Finance    | 7000.00<\/code><\/pre>\n\n\n\n
    \u67e5\u8be2\u5e73\u5747\u5de5\u8d44\u5927\u4e8e 5500 \u7684\u90e8\u95e8\uff1a<\/p>\n\n\n\n
    SELECT department, AVG(salary) AS avg_salary\nFROM employees \nGROUP BY department \nHAVING AVG(salary) > 5500;<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    8. \u8fde\u63a5\u67e5\u8be2 (JOIN<\/code>)<\/strong><\/h2>\n\n\n\n
    JOIN<\/code> \u7528\u4e8e\u8fde\u63a5\u591a\u4e2a\u8868\u3002\u5047\u8bbe\u6709\u4e00\u4e2a departments<\/code> \u8868\uff1a<\/p>\n\n\n\n
    CREATE TABLE departments (\n    id SERIAL PRIMARY KEY,\n    name VARCHAR(50)\n);\nINSERT INTO departments (name) VALUES ('HR'), ('IT'), ('Finance');<\/code><\/pre>\n\n\n\n
    employees<\/code> \u8868\u65b0\u589e department_id<\/code>\uff1a<\/p>\n\n\n\n
    ALTER TABLE employees ADD COLUMN department_id INT;\nUPDATE employees SET department_id = 1 WHERE department = 'HR';\nUPDATE employees SET department_id = 2 WHERE department = 'IT';\nUPDATE employees SET department_id = 3 WHERE department = 'Finance';<\/code><\/pre>\n\n\n\n
    8.1 \u5185\u8fde\u63a5 (INNER JOIN<\/code>)<\/strong><\/h3>\n\n\n\n
    \u67e5\u8be2\u5458\u5de5\u548c\u90e8\u95e8\u4fe1\u606f\uff1a<\/p>\n\n\n\n
    SELECT employees.name, employees.age, departments.name AS department \nFROM employees \nINNER JOIN departments ON employees.department_id = departments.id;<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    9. \u5b50\u67e5\u8be2<\/strong><\/h2>\n\n\n\n
    \u67e5\u8be2\u6bd4\u6240\u6709 HR<\/code> \u5458\u5de5\u5de5\u8d44\u9ad8\u7684\u5458\u5de5\uff1a<\/p>\n\n\n\n
    SELECT * FROM employees WHERE salary > (SELECT MAX(salary) FROM employees WHERE department = 'HR');<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    10. DISTINCT<\/code> \u53bb\u91cd<\/strong><\/h2>\n\n\n\n
    \u67e5\u8be2\u4e0d\u540c\u7684\u90e8\u95e8\uff1a<\/p>\n\n\n\n
    SELECT DISTINCT department FROM employees;<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    11. CASE<\/code> \u8bed\u53e5<\/strong><\/h2>\n\n\n\n
    \u4e3a\u5458\u5de5\u5206\u7c7b\uff1a<\/p>\n\n\n\n
    SELECT name, age, \n    CASE \n        WHEN age < 30 THEN 'Young'\n        WHEN age BETWEEN 30 AND 40 THEN 'Middle-aged'\n        ELSE 'Senior'\n    END AS age_group\nFROM employees;<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    12. SELECT INTO<\/code> \u590d\u5236\u8868<\/strong><\/h2>\n\n\n\n
    \u521b\u5efa backup_employees<\/code> \u5e76\u590d\u5236\u6570\u636e\uff1a<\/p>\n\n\n\n
    SELECT * INTO backup_employees FROM employees;<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    13. WITH<\/code> \u516c\u7528\u8868\u8868\u8fbe\u5f0f (CTE)<\/strong><\/h2>\n\n\n\n
    \u67e5\u8be2\u85aa\u8d44\u9ad8\u4e8e\u5e73\u5747\u5de5\u8d44\u7684\u5458\u5de5\uff1a<\/p>\n\n\n\n
    WITH high_salary_employees AS (\n    SELECT * FROM employees WHERE salary > (SELECT AVG(salary) FROM employees)\n)\nSELECT * FROM high_salary_employees;<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    14. UNION<\/code> \u5408\u5e76\u591a\u4e2a\u67e5\u8be2\u7ed3\u679c<\/strong><\/h2>\n\n\n\n
    \u67e5\u8be2\u6240\u6709\u5458\u5de5\u7684 name<\/code> \u548c department<\/code>\uff1a<\/p>\n\n\n\n
    SELECT name, department FROM employees\nUNION\nSELECT 'John Doe', 'Admin';<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    15. \u603b\u7ed3<\/strong><\/h2>\n\n\n\n
    SQL \u8bed\u6cd5<\/th>\u8bf4\u660e<\/th><\/tr><\/thead>
    SELECT * FROM table;<\/code><\/td>\u67e5\u8be2\u6240\u6709\u6570\u636e<\/td><\/tr>
    SELECT column1, column2 FROM table;<\/code><\/td>\u67e5\u8be2\u6307\u5b9a\u5217<\/td><\/tr>
    SELECT * FROM table WHERE condition;<\/code><\/td>\u6761\u4ef6\u67e5\u8be2<\/td><\/tr>
    SELECT * FROM table ORDER BY column ASC\/DESC;<\/code><\/td>\u6392\u5e8f<\/td><\/tr>
    SELECT * FROM table LIMIT n OFFSET m;<\/code><\/td>\u5206\u9875<\/td><\/tr>
    SELECT COUNT(*) FROM table;<\/code><\/td>\u7edf\u8ba1\u603b\u6570<\/td><\/tr>
    SELECT column, AVG(value) FROM table GROUP BY column;<\/code><\/td>\u5206\u7ec4\u805a\u5408<\/td><\/tr>
    SELECT * FROM table1 INNER JOIN table2 ON condition;<\/code><\/td>\u8fde\u63a5\u67e5\u8be2<\/td><\/tr>
    SELECT * FROM table WHERE column > (SELECT MAX(column) FROM table2);<\/code><\/td>\u5b50\u67e5\u8be2<\/td><\/tr>
    SELECT DISTINCT column FROM table;<\/code><\/td>\u53bb\u91cd\u67e5\u8be2<\/td><\/tr>
    WITH cte AS (...) SELECT * FROM cte;<\/code><\/td>\u516c\u7528\u8868\u8868\u8fbe\u5f0f<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    PostgreSQL SELECT<\/code> \u8bed\u53e5\u529f\u80fd\u5f3a\u5927\uff0c\u9002\u7528\u4e8e\u591a\u79cd\u67e5\u8be2\u9700\u6c42\u3002\u66f4\u591a\u8be6\u7ec6\u5185\u5bb9\u8bf7\u5173\u6ce8\u5176\u4ed6\u76f8\u5173\u6587\u7ae0\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"
    SELECT \u8bed\u53e5\u7528\u4e8e\u4ece PostgreSQL \u6570\u636e\u5e93\u4e2d\u67e5\u8be2\u6570\u636e\uff0c\u662f SQL \u4e2d\u6700\u5e38\u7528\u7684\u67e5\u8be2\u8bed\u53e5\u3002Postgr […]<\/p>\n","protected":false},"author":1,"featured_media":2611,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[78],"tags":[],"class_list":["post-2610","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-postgresql"],"_links":{"self":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/2610","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/comments?post=2610"}],"version-history":[{"count":1,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/2610\/revisions"}],"predecessor-version":[{"id":2612,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/2610\/revisions\/2612"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media\/2611"}],"wp:attachment":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media?parent=2610"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/categories?post=2610"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/tags?post=2610"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}